CIS Fluentd Benchmark

This recommendation verifies that Fluentd is running the latest stable version on the Fluentd log aggregation framework. Implementing this control strengthens the overall security configuration and reduces exposure to potential threats.

Failure to implement this control may leave the Fluentd log aggregation framework vulnerable to attack or non-compliant with organizational security policies. This control helps establish a consistent, hardened configuration baseline.

# Verify Fluentd version
fluentd --version
td-agent --version 2>/dev/null

# Install latest Fluentd
curl -fsSL https://toolbelt.treasuredata.com/sh/install-ubuntu-noble-fluent-package5-lts.sh | sh
# Or via gem:
gem install fluentd --no-document

This recommendation verifies that Fluentd runs as a dedicated non-root user on the Fluentd log aggregation framework. Implementing this control strengthens the overall security configuration and reduces exposure to potential threats.

Failure to implement this control may leave the Fluentd log aggregation framework vulnerable to attack or non-compliant with organizational security policies. This control helps establish a consistent, hardened configuration baseline.

# Check Fluentd runs as dedicated user
ps -eo user,pid,comm | grep -E 'fluentd|td-agent'
grep -E '^User|^Group' /etc/systemd/system/fluentd.service 2>/dev/null

# Run as dedicated non-root user
useradd -r -s /usr/sbin/nologin fluentd
chown -R fluentd:fluentd /etc/fluentd/
chown -R fluentd:fluentd /var/log/fluentd/

This recommendation verifies that input sources use TLS with client certificate auth on the Fluentd log aggregation framework. Implementing this control strengthens the overall security configuration and reduces exposure to potential threats.

Failure to implement this control may leave the Fluentd log aggregation framework vulnerable to attack or non-compliant with organizational security policies. This control helps establish a consistent, hardened configuration baseline.

# Check input source configuration
grep -E '<source>|@type|bind|port' /etc/fluentd/fluent.conf | head -20

# Secure input sources
<source>
  @type forward
  port 24224
  bind 127.0.0.1
  <transport tls>
    cert_path /etc/fluentd/ssl/cert.pem
    private_key_path /etc/fluentd/ssl/key.pem
    ca_path /etc/fluentd/ssl/ca.pem
    client_cert_auth true
  </transport>
  <security>
    self_hostname fluentd-server
    shared_key s3cureK3y
  </security>
</source>

This recommendation verifies that output destinations use TLS with hostname verification on the Fluentd log aggregation framework. Implementing this control strengthens the overall security configuration and reduces exposure to potential threats.

Failure to implement this control may leave the Fluentd log aggregation framework vulnerable to attack or non-compliant with organizational security policies. This control helps establish a consistent, hardened configuration baseline.

# Check output destination TLS
grep -E '<match|<store|tls|ssl' /etc/fluentd/fluent.conf | head -20

# Configure TLS for outputs
<match **>
  @type forward
  <server>
    host aggregator.example.com
    port 24224
  </server>
  <security>
    self_hostname fluentd-client
    shared_key s3cureK3y
  </security>
  transport tls
  tls_cert_path /etc/fluentd/ssl/ca.pem
  tls_verify_hostname true
</match>

This recommendation verifies that file-based buffering with size limits is configured on the Fluentd log aggregation framework. Implementing this control strengthens the overall security configuration and reduces exposure to potential threats.

Failure to implement this control may leave the Fluentd log aggregation framework vulnerable to attack or non-compliant with organizational security policies. This control helps establish a consistent, hardened configuration baseline.

# Check buffer configuration
grep -A10 '<buffer>' /etc/fluentd/fluent.conf

# Configure secure buffering
<buffer>
  @type file
  path /var/log/fluentd/buffer/
  flush_interval 5s
  flush_thread_count 2
  retry_max_times 10
  retry_wait 1s
  chunk_limit_size 8m
  total_limit_size 512m
  overflow_action drop_oldest_chunk
</buffer>

This recommendation verifies that sensitive data is filtered from log streams on the Fluentd log aggregation framework. Implementing this control strengthens the overall security configuration and reduces exposure to potential threats.

Failure to implement this control may leave the Fluentd log aggregation framework vulnerable to attack or non-compliant with organizational security policies. This control helps establish a consistent, hardened configuration baseline.

# Check filtering for sensitive data
grep -E '<filter|record_transformer|grep' /etc/fluentd/fluent.conf

# Filter sensitive data from logs
<filter **>
  @type record_transformer
  remove_keys password,secret,token,authorization,cookie
</filter>
<filter **>
  @type grep
  <exclude>
    key message
    pattern /password|credit_card|ssn/i
  </exclude>
</filter>

This recommendation verifies that structured internal logging is configured on the Fluentd log aggregation framework. Implementing this control strengthens the overall security configuration and reduces exposure to potential threats.

Failure to implement this control may leave the Fluentd log aggregation framework vulnerable to attack or non-compliant with organizational security policies. This control helps establish a consistent, hardened configuration baseline.

# Check Fluentd internal logging
grep -E 'log_level|<system>' /etc/fluentd/fluent.conf

# Configure internal logging
<system>
  log_level info
  suppress_repeated_stacktrace true
  emit_error_log_interval 30s
  <log>
    format json
    time_format %Y-%m-%dT%H:%M:%S%z
  </log>
</system>

This setting ensures that monitoring endpoint is restricted to localhost on the Fluentd log aggregation framework. Restricting this capability limits potential abuse and enforces the principle of least privilege across the environment.

Unrestricted access to this capability could allow unauthorized users or processes to perform actions beyond their intended scope. Applying least-privilege principles to the Fluentd log aggregation framework is essential for defense in depth.

# Check monitoring endpoint
grep -E 'monitor_agent|prometheus' /etc/fluentd/fluent.conf

# Configure monitoring endpoint (restricted)
<source>
  @type monitor_agent
  bind 127.0.0.1
  port 24220
</source>
# Or use Prometheus plugin:
<source>
  @type prometheus
  bind 127.0.0.1
  port 24231
  metrics_path /metrics
</source>

This recommendation verifies that system resource limits are configured on the Fluentd log aggregation framework. Implementing this control strengthens the overall security configuration and reduces exposure to potential threats.

Failure to implement this control may leave the Fluentd log aggregation framework vulnerable to attack or non-compliant with organizational security policies. This control helps establish a consistent, hardened configuration baseline.

# Check system resource limits
grep -E 'workers|root_dir' /etc/fluentd/fluent.conf
ulimit -n

# Configure system resource limits
<system>
  workers 4
  root_dir /var/log/fluentd
</system>
# In systemd unit or limits.conf:
# LimitNOFILE=65536
# Set appropriate process limits

This recommendation verifies that error handling with secondary outputs is configured on the Fluentd log aggregation framework. Implementing this control strengthens the overall security configuration and reduces exposure to potential threats.

Failure to implement this control may leave the Fluentd log aggregation framework vulnerable to attack or non-compliant with organizational security policies. This control helps establish a consistent, hardened configuration baseline.

# Check error handling
grep -E 'error_label|secondary' /etc/fluentd/fluent.conf

# Configure error handling with secondary output
<label @ERROR>
  <match **>
    @type file
    path /var/log/fluentd/error/
    append true
    <buffer>
      flush_interval 10s
    </buffer>
  </match>
</label>
# Add secondary output to critical matches:
<match important.**>
  @type forward
  <secondary>
    @type file
    path /var/log/fluentd/secondary/
  </secondary>
</match>

This recommendation ensures that only required plugins are installed with pinned versions on the Fluentd log aggregation framework. Enforcing this requirement establishes a minimum security standard and prevents insecure configurations.

Without this enforcement, the Fluentd log aggregation framework may accept insecure configurations that weaken overall security posture. Mandating this control ensures consistent protection against common attack vectors.

# Check plugin list
fluent-gem list | head -30

# Audit and restrict plugins
fluent-gem list
# Remove unused plugins:
fluent-gem uninstall fluent-plugin-unused
# Only install plugins from trusted sources
# Pin plugin versions:
fluent-gem install fluent-plugin-elasticsearch -v 5.4.3

This recommendation verifies that secrets are not stored in plaintext configuration on the Fluentd log aggregation framework. Implementing this control strengthens the overall security configuration and reduces exposure to potential threats.

Failure to implement this control may leave the Fluentd log aggregation framework vulnerable to attack or non-compliant with organizational security policies. This control helps establish a consistent, hardened configuration baseline.

# Check for plaintext secrets in config
grep -rn 'password\|secret\|key' /etc/fluentd/ | grep -v '#'

# Use environment variables or key management
# In fluent.conf:
# shared_key "#{ENV['FLUENTD_SHARED_KEY']}"
# Or use Fluentd's secret management:
# In systemd EnvironmentFile:
# EnvironmentFile=/etc/fluentd/fluentd.env
chmod 600 /etc/fluentd/fluentd.env

This recommendation verifies that configuration is validated before reload on the Fluentd log aggregation framework. Implementing this control strengthens the overall security configuration and reduces exposure to potential threats.

Failure to implement this control may leave the Fluentd log aggregation framework vulnerable to attack or non-compliant with organizational security policies. This control helps establish a consistent, hardened configuration baseline.

# Check configuration validity
fluentd --dry-run -c /etc/fluentd/fluent.conf

# Validate config before reload
fluentd --dry-run -c /etc/fluentd/fluent.conf
if [ $? -eq 0 ]; then
    systemctl reload fluentd
fi

This setting ensures that configuration file permissions are restricted on the Fluentd log aggregation framework. Restricting this capability limits potential abuse and enforces the principle of least privilege across the environment.

Unrestricted access to this capability could allow unauthorized users or processes to perform actions beyond their intended scope. Applying least-privilege principles to the Fluentd log aggregation framework is essential for defense in depth.

# Check file permissions
stat -c '%a %U %G' /etc/fluentd/fluent.conf
find /etc/fluentd -type f -exec stat -c '%a %n' {} \;

# Restrict file permissions
chmod 640 /etc/fluentd/fluent.conf
chown root:fluentd /etc/fluentd/fluent.conf
chmod 750 /etc/fluentd/
chmod 750 /var/log/fluentd/